The present invention generally relates to contaminated liquid mixing apparatus. More particularly, the present invention relates to a contaminated mixing apparatus which is adjustable for precise and controlled mixing of contaminants and treatment additives in the form of gases and fluids, so as to create a generally homogenous mixture having a high bubble or gas entrainment level.
Industrial wastewater treatment presents many challenges to current technologies. Contaminants are often present in the form of suspended solids. Such solids range in size from macroscopic, hundreds of microns to inches in size, to colloidal, or sub-micron in size, or even nanoscopic particles. Immiscible oils and other oil loving substances, generally termed hydrophobic, are also sometimes present. In treating contaminated water such as wastewater or the like resulting from agricultural or industrial processes, it is necessary to mix treatment additives with the contaminated water in order to effectively remove the contaminants.
Numerous technologies have been developed to achieve efficient solid/liquid separation in industrial wastewater treatment facilities. Historically, gravimetric separations are most commonly used. Sedimentation enlarged clarifier tanks are used to separate particles with specific gravities greater than that of water. Screens and filters can be used to separate large particles as well. However, smaller particles and other substances, such as hydrophobic substances which are sometimes present and emulsified or solubilized and thus have a density closer to that of the liquid, typically water, are much more difficult to remove.
Typically, such solubilized contaminated water is treated using flotation systems. Flotation is a process in which one or more specific particle constituents of a slurry or suspension of finely dispersed particles or droplets become attached to gas bubbles so that they can be separated from water or other constituents. The gas/particle aggregates then float to the top of the flotation vessel where they may be separated from water and other non-floatable constituents.
Most wastewater solid and emulsified components such as soil particles, fats, oils and grease are charged. Wastewater processing/treatment chemicals or additives such as coagulants and flocculents are added to neutralize charge and initiate nucleation and growth of larger colloidal and suspended particles, also referred to as floccs. Floccs can arrange in size from a millimeter to centimeters in diameter when coagulation and flocculation processes are optimized. Too much chemical will recharge floccs and result in their break-up and/or permanent destruction as overcharged particles or floccs repel each other and tend to stay apart.
It is preferred that the contaminated liquid and treatment additives form a homogenous mixture such that when the dissolved gas is added and subsequently allowed to coalesce into bubbles, a good majority of the contaminants will be taken into the surface with the bubbles. If the mixture is not homogenous, an unacceptable amount of contaminants will remain in the liquid even after treatment.
In the past, treatment additives have been added to contaminated liquid in several manners. For example, treatment additives are often mixed into a tank of contaminated liquid and then mechanically stirred with a propeller or the like. However, it has been found that the treatment additives tend to “glob” to each other prematurely.
Coagulants are chemicals used to neutralize particle charge such as inorganic salts (e.g. ferric chloride) or polymers (e.g. cationic polyamines). Flocculants are large molecular weight polymers used to collect the smaller coagulated floccs into large stable floccs, facilitating solid/liquid separation. These large molecules are often coiled and have to be uncoiled plus mixed well with the incoming coagulated wastewater stream.
Coagulants are often viscous chemicals, requiring adequate mixing time and energy to mix them homogeneously with the incoming wastewater stream. Similarly, an optimum mixing energy is required for the flocculants to be uncoiled and mixed well with the incoming coagulated wastewater stream. If the polymer strands are wound or “globbed” together, the polymer can only attach a minimal amount of waste particles. If mixing is not optimized, an excessive amount of coagulant or flocculant polymer may be introduced into the contaminated liquid in an attempt to coagulate to the greatest extent possible, thus wasting valuable and expensive coagulant and polymer chemicals. However, if too much mixing energy is applied, irreversible break-up of the floccs and inefficient solid/liquid separation occurs.
In the past, it was believed that vigorous mixing over a prolonged period of time provided optimal mixing. However, the inventors have found that this is not the case. Instead, the inventors have discovered that certain treatment additives are very sensitive to the amount of mixing energy that is used. Thus, overmixing, as well as undermixing, can have deleterious effects on the additives and may alter their behavior or efficiency. The inventors have also found that mixing time for various treatment additives vary according to the mixing energy used. To effectively use coagulants and flocculants, mixing time and energy must be matched with pressurization and depressurization energy to create bubbles that are the right size to attach to the floccs and create bubbles that grow into larger bubbles after attaching to the floccs. This ensures the flotation of the flocc clusters out of the water and replacement of much of the entrained water in the flocc cluster with air.
Current technologies are not satisfactory in their ability to respond fast to a changing wastewater influent. The mixing of chemical additives is often physically destructive. It is often not efficient and generally requires a long time, causing the real life systems to be large and take up valuable real estate inside the manufacturing facilities.
Accordingly, there is a need for a mixing apparatus which is adjustable in nature so as to allow one to easily adjust the pressurization or mixing energy of a given waste water stream as its characteristics change or which can be modified between different treatment facilities which treat different wastewater streams. Such a mixing apparatus should require less additives and facilitate optimum removal of the contaminants from the liquid. The present invention fulfills these needs and provides other related advantages.